The present invention generally relates to a paper transport apparatus employed in an image forming apparatus such as an electrophotographic, or xerographic copying machine capable of forming a double-face (duplex) copy. More specifically, the present invention is directed to a paper transport apparatus equipped with such a paper processing means so that when a paper jam occurs in a paper transport path, copy paper, which is ejectable as a double-face copy, is transported toward an ejection tray. Thus, the amount of jammed copy paper removed from the paper transport path is reduced as much as possible.
In an image forming apparatus such as an electrophotographic copying machine and a laser beam printer, there is typically provided an apparatus for forming an image on one surface of the paper to provide a single-face copy, and another apparatus for forming images on both surfaces (front/rear faces) of the paper to provide a double-face copy. In the automatic double-face copying machine, as disclosed in Japanese Laid-open Patent Application No. 2-239058 (opened in 1990), the copying machine is constructed so that copy paper formed as a single-face copy is inverted to transfer an image on a rear surface of the paper, thereby forming a double-face copy. The inverting transport path is provided in the automatic double-face copying machine so that one image may be transferred to the front face (first face) of the copy paper stored in the paper supply unit in order to obtain the single-face copy paper, and so that the single-face copy paper may be inverted to transfer another image to the rear face (second face) in order to obtain the double-face copy paper. Both the operation of transferring the image to the first face of the paper fed from the paper supply tray, and the operation of transferring the image to the second face of this single-face copy paper are alternately repeated.
When a so-called "paper jam" occurs in the paper transport path and the copy paper [hereinafter referred to as "jammed paper"] is stopped within the paper transport path in the automatic double-face copying machine, all operations of the copying machine are interrupted so that the copying machine can issue a demand for removal of the jammed paper to the control panel. However, if the copy paper remains within the image fixing apparatus when the jammed paper is stopped in the paper transport path, then a problem is produced. Furthermore, since most double-face copying machines include a control system which requests the commencement of a newly formed single-face copy when all of the copy paper left in the paper transport path is removed after a paper jam occurs, a heavy burden is placed on the operator and a large amount of copy paper is wasted.
To solve these problems, the conventional copying machine, as described in Japanese Laid-open Patent Application No. 2-239058, is stopped when the image writing error occurs, and the operation mode is switched from the inverting path to the ejecting path in order to process the copy paper. As described in Japanese Laid-open Patent Application No. 2-257158, when the paper jam occurs in the invert-transport path, the copy paper remaining in the paper transport path is automatically removed from the paper ejecting port located in front of the paper transport path. With the employment of the above-described automatic paper ejecting method, only the jammed paper is removed from the paper transport path, so that the paper jamming problem can be solved and the copying machine can be easily restarted.
As explained in connection with the prior art, in the relatively compact image forming apparatus, the amount of copy paper transported through the paper transport path is small, and the amount of jammed copy paper wasted during the paper jam processing operation is also small. Further, the amount of reformed copy paper is small. For example, in the copying machine disclosed in Japanese Laid-open Patent Application No. 2-239058, when a printing error occurs, only one sheet of copy paper is wasted and the subsequent printing operation can be readily recovered. In contrast, as explained in Japanese Laid-open Patent Application No. 2-257158, when paper jamming occurs in the invert-transport path, a means for ejecting the single-face copy paper and a means for directly ejecting paper upon which no image has been transferred are employed. However, the transport means for storing the single-face copy paper must be provided separately from the main body of the copying machine. Another problem is that the construction of the paper transport apparatus is complex. A further problem is that the single-face copy paper stored in the ejection tray provided in the copy machine is discarded, and therefore a heavy burden is placed on the operator since a new copy must be formed to replace the discarded single-face copy paper sheets.
In a relatively large-scale, automatic, double-face copying machine, 5 to 6 sheets (i.e., large numbers) of copy paper are transported within the paper transport path. When paper jamming occurs in the paper transport path, a large number of sheets of copy paper needs to be removed. After the jammed paper has been removed from the paper transport path, a new copy is required to be generated, so that a heavy burden is placed on the operator. In the worst case, there is the potential that all of the copies would have to be regenerated. Also, when the copy paper, whose first plane has been copied, is jammed in the transport path, very cumbersome processing operations are required to remove the jammed paper and the copy paper preceding and succeeding the jammed paper.
For instance, before the double-face copy paper is to be ejected, the single-face copy paper may be exhausted to the purge tray. However, there are two different methods to accomplish this. The single-face copy paper located up stream from the jammed paper is stopped at its present position, or a copy paper ejecting means is provided. However, there is the problem that when the transportation of the single-face copy paper up stream from the jammed paper is stopped, both the jammed paper and the copy paper located up stream are removed from the paper transport path, resulting in a large amount of wasted copy paper. A further problem is that since the copy paper is rejected by using the purge tray, these copies are ejected under such a condition that the single-face copy paper is mixed with the double-face copy paper, placing a very heavy burden on the operator so as to process the subsequent copy paper.
In addition to the above-described problems, a paper invert-ejecting mechanism having a copy ejecting unit is provided for the automatic double-face copying machine so as to constitute a multifunctional copying machine. However, when the copy invert-ejecting mechanism is arranged with an inverting path and a paper jam occurs, all of the copy paper present up stream from the paper jam are stopped. Thus, the paper located in the image fixing apparatus could be burned by heat of the heat roller. To avoid such a problem, it is possible for the paper located within the image fixing apparatus to be forcibly transported along the copy ejecting direction, whereby the adverse influences of the heat roller may be eliminated, and the cumbersome operation of removing the remaining paper from the image fixing apparatus may be omitted. However, it is difficult to employ such a method since the copy paper forcibly fed out will collide with the copy paper stopped at the ejecting unit, and thus worsen the jamming condition. Also, since the paper transport intervals within the paper transport path are separated from each other in the conventional automatic double-face copying machine, it is not possible for the subsequent copy paper to be injected into the image fixing apparatus while a single sheet of copy paper is located in the inverting path.